A radial reactor comprises a cylindrical reactor body containing specially designed reactor internals. The main reactor internals that provide the radial flow pattern in a conventional radial flow fixed bed reactor are an inlet barrier (pie plates), an inlet distributing header and an axial outlet collecting header. The two primary types of inlet distributors include wedge wire screens and series of scallops, with each scallop comprising a perforated half cylinder having a relatively small diameter positioned around the circumference of the vessel. The axial outlet collecting header may be in the form of a perforated cylinder or ‘centerpipe’. Catalyst is generally charged to an annular space positioned between the inlet distributing header and the centerpipe, and the top of the catalyst bed is covered with a cover plate.
Depending on the axial direction of the flow in the distributing channel and the centerpipe, radial flow reactors may be classified as z-flow type or π-flow type. Depending on the radial flow direction in the reactor, radial flow reactors can be further classified into centripetal (CP) or centrifugal (CF) flow types. In the CP-flow type, gas is fed to the distributing channel and travels radially from the outer screen to the centerpipe, while in the CF-flow type, gas is fed to the centerpipe and travels radially from the centerpipe to the outer screen. Four flow configurations are thus typical for conventional radial flow reactors; these can be classified as CP-z, CP-π, CF-z and CF-π configurations.
Conventional radial flow reactors thus comprise a single catalyst bed, with gas feed being introduced into the distributing channel or the centerpipe and product being removed in the same or the opposite axial direction from the centerpipe or the distributing channel following passage through the single catalyst bed.
Radial flow reactors are often utilized to carry out endothermic reactions. Reforming reactions, such as the AROMAX® Process by Chevron Phillips Chemical Company LP, The Woodlands, Tex., are extremely endothermic. As vaporized feed transits the reactor bed (e.g., from the wire screen or the scallops to the centerpipe), the temperature of the catalyst may quickly drop below the activation temperature for the dehydrogenation reactions. As working catalyst deactivates, the reactor inlet temperature is increased in order to compensate for loss of activity. The deactivated catalyst is also a less selective catalyst and has significant activity for hydrocarbon cracking reactions. This deactivated catalyst is also at the higher temperature which also results in more cracked products being produced. The cracked products represent a significant downgrade from the value of the more expensive feed (valued as a gasoline blendstock) to light hydrocarbons (valued as fuel gas). Economic end of run is then met when the amount of value lost to light hydrocarbons by cracking is greater than or equal to the cost of replacing the catalyst and the cost of the lost production during the replacement. When economic end of run criteria is reached much of the catalyst near the vapor outlet zone is not fully utilized.
Accordingly, there exists a need for improved radial flow reactors, as well as systems and methods employing such reactors. Desirably, such reactors, systems and methods enable improved catalyst utilization, minimized downtime, and/or minimized coking.